![]() ![]() Cycling this cap tells you how strong the pullup is. The above can be calibrated by adding one more cap on board with cap > stray and pin capacitance. Weak pullups vary in current sourcing by ? 2:1 ratio. Can be 0402 if desired (breathing hazard :-) ) Pin can even be used for other purposes if desired if cap not too large. ![]() Needs: One capacitor, relatively low value. ![]() Repeat several times if desired to check value.Ĭan be multicycle oscillator or single cycle. Measure time taken to go high as cap is charged by weak pullups. With care this gives minimal cost, minimal area, no power drain except when testing (and hardly then), no EMI etc when not in use. Exponential charge of a capacitor using weak pullups, preceded by discharge of capacitor. Software driven sawtooth oscillation cycle. Esaki / Tunnel diode and R !!! :-).īUT if you want something smaller and cheaper and electronic that arguably satisfies the letter and spirit of you requirement even though it does not look like an oscillator in isolation, and that requires a single 0402 packaged 1 cent component then. Neon and cap and resistor if getting desperate. A unijunction forms a relaxation oscillator with a very few parts. You could also use an opamp or comparator for the same purpose. You can use a pkg of 6 gates for lowest cost (as they are so common) or for minimum size use some of the tiny single gate packages. If I wanted a "real" standalone oscillator then something like Steven's Schmitt trigger gate (which I also mentioned in the monostable query) is a practical cheap and flexible electronic solution. ![]()
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